Phentermine one of the most prescribed weight-loss medicines. Phentermine is used for weight reduction in patients with obesity.it is used in patients with obesity.the average weight loss when taking phentermine is 3% of your initial body weight after 3 months and 5-7 after 6 months.take the medication by mouth as directly by your doctor usually once a day.take a six months this tablet long term safety. Qsymia is likely the most effective prescription weight loss pill. This tablets are used adult and children